1. Field of the Invention
The present invention relates to a random error distribution evaluation method for evaluating error distribution of a digital signal which includes error data which is randomly generated at a predetermined error rate, and an evaluation apparatus thereof and, more particularly, to a random error distribution evaluation method arid random error distribution evaluation apparatus for quantitatively evaluating a degree of approximation (conformity) of error distribution of a digital signal which is measured as a measurement object, to the Poisson distribution.
2. Description of the Related Art
In a testing apparatus for carrying out various tests on various communication equipments which are incorporated in a digital communication network using a general electric signal cable or an optical communication network using an optical fiber cable, a test signal appropriate for the actual status of use of a communication equipment is input to the communication equipment which is a measurement object to be tested, and a response operation of the communication equipment is evaluated In one of evaluation tests for such communication equipment, there is employed a test signal which is intentionally subjected to contain error or errors, as a test signal which is appropriate for the actual status of use of the communication equipment and is supplied to the communication equipment to be measured. Further, it is evaluated to what degree of the rate of occurrence of the error (error rate) E, the communication equipment operates normally, the error being contained in the test signal.
An occurrence rate (error rate) E of an error (error bit) usually contained is of the order of E=10−2 to 10−8, which is produced due to any factor including external noise and the like, in various digital signals to be transmitted/received in a communication network not for connecting general user terminals and a base station or subscriber terminals and a telephone office but for connecting stations to each other. Furthermore, the error occurs randomly.
Accordingly, in the testing apparatus, a random error signal generation circuit for generating a random error signal for causing an error of, for example, a bit of “1” at a designated error occurrence rate E, and furthermore at random is incorporated in addition to a test signal generation circuit for generating an original digital. test signal. Further, an EXCLUSIVE-OR operation of the digital test signal output from the test signal generation circuit and a random error signal output from the random error signal generation circuit is carried out, and the operation result is inverted, whereby a test signal containing an error of the designated error occurrence rate E is created.
It is proved that the occurrence frequency of events that incidentally occur in the natural world substantially follows the Poisson distribution. Accordingly, the distribution of errors contained in the various digital signals to be transmitted from/to a station of the above-mentioned communication network to/from another station thereof on the temporal axis also follows the Poisson distribution. For this reason, it is desirable that the error distribution of the random error signal generated by the random error signal generation circuit incorporated in the testing apparatus should also follow the Poisson distribution.
An example of the error signal generation circuit for generating a Poisson distribution error signal having error distribution of the Poisson distribution is proposed in Pat. Document 1 described below. Further, in Non-Pat. Document 1 also described below, there is disclosed fundamental logic theory for the chi-square goodness-of-fit determination method of quantitatively determining whether or not the statistically obtained occurrence distribution of an event conforms to the theoretical distribution
Pat. Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2002-330192
Non-Pat. Document 1: J. Gutman/S.C. Wils, joint translation by Ishii/Hori, BAIFUKAN CO., LTD, 1968, “Outline of Statistics” for engineers